Adjustable extended electrode for edge uniformity control

ABSTRACT

Embodiments described herein generally related to a substrate processing apparatus. In one embodiment, a process kit for a substrate processing chamber disclosed herein. The process kit includes a first ring having a top surface and a bottom surface, an adjustable tuning ring having a top surface and a bottom surface, and an actuating mechanism. The bottom surface is supported by a substrate support member. The bottom surface at least partially extends beneath a substrate supported by the substrate support member. The adjustable tuning ring is positioned beneath the first ring. The top surface of the adjustable tuning ring and the first ring define an adjustable gap. The actuating mechanism is interfaced with the bottom surface of the adjustable tuning ring. The actuating mechanism is configured to alter the adjustable gap defined between the bottom surface of the first ring and the top surface of the adjustable tuning ring.

BACKGROUND Field

Embodiments described herein generally relate to a substrate processingapparatus, and more specifically to an improved process kit for asubstrate processing apparatus.

Description of the Related Art

As semiconductor technology nodes advanced with reduced size devicegeometries, substrate edge critical dimension uniformity requirementsbecome more stringent and affect die yields. Commercial plasma reactorsinclude multiple tunable knobs for controlling process uniformity acrossa substrate, such as, for example, temperature, gas flow, RF power, andthe like. Typically, in etch processes, silicon substrates are etchedwhile electrostatically clamped to an electrostatic chuck.

During processing, a substrate resting on a substrate support mayundergo a process that deposits material on the substrate and to remove,or etch, portions of the material from the substrate, often insuccession or in alternating processes. It is typically beneficial tohave uniform deposition and etching rates across the surface of thesubstrate. However, process non-uniformities often exist across thesurface of the substrate and may be significant at the perimeter or edgeof the substrate. These non-uniformities at the perimeter may beattributable to electric field termination affects and are sometimesreferred to as edge effects. During deposition or etching, a process kitcontaining at least a deposition ring is sometimes provided to favorablyinfluence uniformity at the substrate perimeter or edge.

Accordingly, there is a continual need for an improved process kit for asubstrate processing apparatus.

SUMMARY

Embodiments described herein generally related to a substrate processingapparatus. In one embodiment, a process kit for a substrate processingchamber disclosed herein. The process kit includes a first ring, anadjustable tuning ring, and an actuating mechanism. The first ring has atop surface and a bottom surface. The bottom surface is supported by asubstrate support member. The bottom surface at least partially extendsbeneath a substrate supported by the substrate support member. Theadjustable tuning ring is positioned beneath the first ring. Theadjustable tuning ring has a top surface and a bottom surface. The topsurface of the adjustable tuning ring and the first ring define anadjustable gap. The actuating mechanism is interfaced with the bottomsurface of the adjustable tuning ring. The actuating mechanism isconfigured to alter the adjustable gap defined between the bottomsurface of the first ring and the top surface of the adjustable tuningring.

In another embodiment, a processing chamber is disclosed herein. Theprocessing chamber includes a substrate support member and a processkit. The substrate support member is configured to support a substrate.The process kit is supported by the substrate support member. Theprocess kit includes a first ring, an adjustable tuning ring, and anactuating mechanism. The first ring has a top surface and a bottomsurface. The bottom surface is supported by the substrate supportmember. The bottom surface at least partially extends beneath asubstrate supported by the substrate support member. The adjustabletuning ring is positioned beneath the first ring. The adjustable tuningring has a top surface and a bottom surface. The top surface of theadjustable tuning ring and the first ring define an adjustable gap. Theactuating mechanism is interfaced with the bottom surface of theadjustable tuning ring. The actuating mechanism is configured to alterthe adjustable gap defined between the bottom surface of the first ringand the top surface of the adjustable tuning ring.

In another embodiment, a method of processing a substrate is disclosedherein. The substrate is positioned on a substrate support memberdisposed in a substrate processing chamber. A plasma is created above asubstrate. A spacing between an adjustable tuning ring and an edge ringis adjusted by actuating the adjustable tuning ring to change thedirection of the plasma ions at an edge of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

FIG. 1 is a cross sectional view of a processing chamber, according toone embodiment.

FIG. 2A is enlarged partial cross sectional view of the processingchamber of FIG. 1, according to one embodiment.

FIG. 2B is enlarged partial cross sectional view of the processingchamber of FIG. 1, according to one embodiment.

FIG. 3 is a simplified cross sectional view of a portion of theprocessing chamber of FIG. 1 depicting two capacitance paths, accordingto one embodiment.

FIG. 4 is a simplified cross sectional view of a portion of theprocessing chamber of FIG. 1, according to one embodiment, illustratinganother advantage of the present disclosure.

For clarity, identical reference numerals have been used, whereapplicable, to designate identical elements that are common betweenfigures. Additionally, elements of one embodiment may be advantageouslyadapted for utilization in other embodiments described herein.

DETAILED DESCRIPTION

FIG. 1 is a cross sectional view of a processing chamber 100 having anadjustable tuning ring 150, according to one embodiment. As shown, theprocessing chamber 100 is an etch chamber suitable for etching asubstrate, such as substrate 101. Examples of processing chambers thatmay be adapted to benefit from the disclosure are Sym3® ProcessingChamber, C3® Processing Chamber, and Mesa™ Processing Chamber,commercially available from Applied Materials, Inc., located in SantaClara, Calif. It is contemplated that other processing chamber,including deposition chambers and those from other manufacturers, may beadapted to benefit from the disclosure.

The processing chamber 100 may be used for various plasma processes. Inone embodiment, the processing chamber 100 may be used to perform dryetching with one or more etching agents. For example, the processingchamber may be used for ignition of plasma from a precursor CxFy (wherex and y can be different allowed combinations), O2, NF3, or combinationsthereof.

The processing chamber 100 includes a chamber body 102, a lid assembly104, and a support assembly 106. The lid assembly 104 is positioned atan upper end of the chamber body 102. The support assembly 106 isdisclosed in an interior volume 108, defined by the chamber body 102.The chamber body 102 includes a slit valve opening 110 formed in asidewall thereof. The slit valve opening 110 is selectively opened andclosed to allow access to the interior volume 108 by a substratehandling robot (not shown).

The chamber body 102 may further include a liner 112 that surrounds thesupport assembly 106. The liner 112 is removable for servicing andcleaning. The liner 112 may be made of a metal such as aluminum, aceramic material, or any other process compatible material. In one ormore embodiments, the liner 112 includes one or more apertures 114 and apumping channel 116 formed therein that is in fluid communication with avacuum port 118. The apertures 114 provide a flow path for gases intothe pumping channel 116. The pumping channel 116 provides an egress forthe gases within the chamber 100 to vacuum port 118.

A vacuum system 120 is coupled to the vacuum port 118. The vacuum system120 may include a vacuum pump 122 and a throttle valve 124. The throttlevalve 124 regulates the flow of gases through the chamber 100. Thevacuum pump 122 is coupled to the vacuum port 118 disposed in theinterior volume 108.

The lid assembly 104 includes at least two stacked components configuredto form a plasma volume or cavity therebetween. In one or moreembodiments, the lid assembly 104 includes a first electrode 126 (“upperelectrode”) disposed vertically above a second electrode 128 (“lowerelectrode”). The upper electrode 126 and the lower electrode 128 confinea plasma cavity 130, therebetween. The first electrode 126 is coupled toa power source 132, such as an RF power supply. The second electrode 128is connected to ground, forming a capacitance between the two electrodes126, 128. The upper electrode 126 is in fluid communication with a gasinlet 134. The first end of the one or more gas inlets 134 opens intothe plasma cavity 130.

The lid assembly 104 may also include an isolator ring 136 thatelectrically isolates the first electrode 126 from the second electrode128. The isolator ring 136 may be made from aluminum oxide or any otherinsulative, processing compatible, material.

The lid assembly may also include a gas distribution plate 138 and ablocker plate 140. The second electrode 128, the gas distribution plate138, and the blocker plate 140 may be stacked and disposed on a lid rim142, which is coupled to the chamber body 102.

In one or more embodiments, the second electrode 128 may include aplurality of gas passages 144 formed beneath the plasma cavity 130 toallow gas from the plasma cavity 130 to flow therethrough. The gasdistribution plate 138 includes a plurality of apertures 146 configuredto distribute the flow of gases therethrough. The blocker plate 140 mayoptionally be disposed between the second electrode 128 and the gasdistribution plate 138. The blocker plate 140 includes a plurality ofapertures 148 to provide a plurality of gas passages from the secondelectrode 128 to the gas distribution plate 138.

The support assembly 106 may include a support member 180. The supportmember 180 is configured to support the substrate 101 for processing.The support member 180 may be coupled to a lift mechanism 182 through ashaft 184, which extends through a bottom surface of the chamber body102. The lift mechanism 182 may be flexibly sealed to the chamber body102 by a bellows 186 that prevents vacuum leakage from around the shaft184. The lift mechanism 182 allows the support member 180 to be movedvertically within the chamber body 102 between a lower transfer portionand a number of raised process positions. Additionally, one or more liftpins 188 may be disposed through the support member 180. The one or morelift pins 188 are configured to extend through the support member 180such that the substrate 101 may be raised off the surface of the supportmember 180. The one or more lift pins 188 may be active by a lift ring190.

FIG. 2A is a partial cross sectional view of a portion of the processingchamber 100, illustrating a process kit 200 disposed therein on asupport member 180, according to one embodiment. The support member 180includes an electrostatic chuck 202, a cooling plate (or cathode) 204,and a base 206. The cooling plate 204 is disposed on the base 206. Thecooling plate 204 may include a plurality of cooling channels (notshown) for circulating coolant therethrough. The cooling plate 204 maybe engaged with the electrostatic chuck 202 by an adhesive or anysuitable mechanism. One or more power supplies 208 may be coupled to thecooling plate 204. The electrostatic chuck 202 may include one or moreheaters (not shown). The one or more heaters may be independentlycontrollable. The one or more heaters enable the electrostatic chuck 202to heat the substrate 101 from a bottom surface of the substrate 101 toa desired temperature.

The process kit 200 may be supported on the support member 180. Theprocess kit 200 includes an edge ring 210 having an annular body 230.The body 230 includes a top surface 209, a bottom surface 211, and inneredge 232, and an outer edge 234. The top surface 209 is substantiallyparallel to the bottom surface 211. The inner edge 232 is substantiallyparallel to the outer edge 234, and substantially perpendicular to thebottom surface 211. The body 230 further includes a stepped surface 236defined therein. The stepped surface 236 is formed in the inner edge232, such that the stepped surface 236 is substantially parallel to thebottom surface 211. The stepped surface 236 defines a recess forreceiving a substrate (e.g., substrate 101). The edge ring 210 isadapted to cover an outer perimeter of the support member 180 andprotect the support member 180 from deposition.

The process kit 200 may further include a cover ring 212 and a quartzring 214. The cover ring 212 includes an annular body 238 having a topsurface 240, bottom surface 242, inner edge 244, and outer edge 246. Thetop surface 240 is substantially parallel to the bottom surface 242. Theinner edge 244 is substantially parallel to the outer edge 246, andsubstantially perpendicular to the bottom surface 242. In the embodimentshown in FIG. 2A, a notch 248 is formed in the bottom surface 242 of thebody 238. The quartz ring 214 is disposed adjacent the support member180. The quartz ring 214 includes an annular body 251 having a topsurface 252, bottom surface 254, inner edge 256, and outer edge 258. Thequartz ring 214 is configured to support the cover ring 212 in theprocessing chamber 100. For example, in the embodiment shown, the quartzring 214 supports the cover ring 212 from the bottom surface 242 of thecover ring 212. In some embodiments, the quartz ring 214 may include aprotruding member 263. The protruding member 263 protrudes from the topsurface 252 of the quartz ring. The protruding member 263 is configuredto mate with the notch 248 formed in the bottom surface 242 of the coverring 212. The cover ring 212 is positioned along an outside perimeter216 of the edge ring 210. The edge ring 210 is configured to blockparticles from slipping beneath the edge ring 210.

The process kit 200 further includes an adjustable tuning ring 150having a top surface 215 and a bottom surface 217. The adjustable tuningring 150 may be formed from a conductive material, such as aluminum. Theadjustable tuning ring 150 is disposed beneath the edge ring 210,between the quartz ring 214 and the support member 180, forming a gap250. For example, in one embodiment, the adjustable tuning ring 150extends down past the electrostatic chuck 202, alongside the coolingplate 204. In one embodiment, the adjustable tuning ring 150 has aheight that extends all the way to the bottom of the cooling plate 204.As such, the adjustable tuning ring 150 is able to couple power from thecooling plate 204 to the edge ring 210. The adjustable tuning ring 150may circumscribe the cooling plate 204, thus forming a laterally spacedgap 255. In one example, the laterally spaced gap is greater than 0inches and less than or equal to 0.03 inches. The adjustable tuning ring150 interfaces with a lift pin 218. For example, the lift pin 218 may beoperably coupled with the adjustable tuning ring 150. The lift pin 218is driven by the lift mechanism 183. In some embodiments, the lift pin218 may be driven by a lift mechanism (not shown) independent form thelift mechanism 183. The lift mechanism 183 allows the adjustable tuningring 150 to be moved vertically within the chamber 100. In oneembodiment, the adjustable tuning ring may be moved between greater than0 mm and less than or equal to 4 mm vertically, for example, between 2-4mm. Moving the tuning ring 150 vertically changes the RF power couplingwith the edge ring. In one embodiment, the adjustable tuning ring 150may include a coating 281 formed on the top surface 215 of theadjustable tuning ring 150. For example, the coating 281 may be a yttriaoxide coating or a gel-like coating. The coating 281 is used to limitthe chemical reaction between the plasma and the adjustable tuning ring150 and thus limits particle creation and ring damage. In anotherembodiment, one or more dielectric pads (e.g., Teflon pads) 289 arepositioned in between the edge ring 210 and the electrostatic chuck, onwhich the edge ring 210 sits. The one or more dielectric pads 289 createa gap between the edge ring 210 and the electrostatic chuck in order todecrease the capacitance 302 so that the power coupled from the cathodeto the ring 210 is minimized.

In another embodiment, such as that shown in FIG. 2B, the adjustabletuning ring 150 may be moved manually, thus eliminating the need for thelift pin 218. The tuning ring 150 may include a cavity 260 and an accessorifice formed therein. The access orifice 262 is formed from a top ofthe adjustable tuning ring 150, and extends down into the cavity 260.The access orifice 262 has a first diameter 264 that is smaller than asecond diameter 265 of the cavity 260. The cavity 260 is formed beneaththe access orifice 262. The cavity 260 is formed down to a bottom of thetuning ring 150. The cavity 260 is configured to house a screw 266. Thescrew 266 may be turned via a hex key (not shown), for example,extending into the cavity 260 via the access orifice 262 such that thescrew 266 can raise/lower the tuning ring 150.

FIG. 3 is a simplified cross sectional view of a portion of theprocessing chamber of FIG. 1 depicting two capacitances, according toone embodiment. Power may be coupled from the cathode 204 to the edgering along two paths through two capacitances 302, 304. The amount ofpower coupled depends on the capacitance along these two paths. Thecapacitance 302 is fixed. The capacitance 304 may be varied. Forexample, the capacitance 304 can be tuned by moving the adjustabletuning ring 150 under the edge ring 210 in the vertical direction, thusmodifying a gap 250 formed therebetween. Controlling the gap 250 betweenthe adjustable tuning ring 150 and the edge ring 210 controls thecapacitance therebetween. Mathematical, capacitance can be representedas

$C = {ɛ \cdot ɛ_{0} \cdot \frac{Area}{Gap}}$where ∈ represents the dielectric constant of the material between thetwo electrodes (1 for air in the case for the gap 250), ∈₀ representsthe dielectric constant of free space, area represents the area of theadjustable tuning ring 150, and the gap represents the gap 250. Asshown, as the gap decreases, the value for

$\frac{Area}{Gap}$increases, which leads to an increase of the overall capacitance C. Asthe gap increases, i.e., as the adjustable tuning sleeve is movedfarther away from the edge ring 210, the value for

$\frac{Area}{Gap}$decrease, which decreases the overall capacitance C. As such,controlling the gap value alters the capacitance between the edge ring210 and the cathode 204. A change in the capacitance changes the powercoupled between the edge ring 210 and the cathode 204 and therefore thevoltage that is applied to the edge ring 210. For example, as thecapacitance increases from a decrease in the gap 250, the voltageapplied to the edge ring 210 increases. Controlling the voltage appliedto the edge ring 210 allows for control of a plasma sheath about thesubstrate 101 and the edge ring 210. The effect of which, is discussedin more detail below in conjunction with FIG. 4.

FIG. 4 illustrates a portion of the processing chamber 100, according toone embodiment, illustrating another advantage of the presentdisclosure. Adjusting a vertical gap 402 between the adjustable tuningring 150 and the edge ring 210 increases/decreases the voltage appliedto the edge ring 210. The voltage can be used to control plasma sheath404 profile at an edge 406 of the substrate 101 to compensate forcritical dimension uniformity at the substrate edge 406. The plasmasheath 404 is a thin region of strong electric fields formed by spacecharge that joins the body of the plasma to its material boundary.Mathematically, the sheath thickness, d, is represented by theChild-Langmuir equation:

$d = {\frac{2}{3}\left( \frac{ɛ}{i} \right)^{\frac{1}{2}}\left( \frac{2e}{m} \right)^{\frac{1}{4}}\left( {V_{p} - V_{DC}} \right)^{\frac{3}{4}}}$

Where i is the ion current density, ϵ is the permittivity of vacuum, eis the elementary electric charge, V_(p) is the plasma potential, andV_(DC) is the DC voltage.

In the case of an etch reactor, a plasma sheath 404 is formed betweenthe plasma and the substrate 101 being etched, the chamber body 102, andevery other part of the processing chamber 100 in contact with theplasma. The ions produced in a plasma are accelerated in the plasmasheath and move perpendicular to the plasma sheath. Controlling theV_(DC), i.e., controlling the voltage applied to the edge ring 210,affects the thickness, d, of the sheath 404. For example, as the voltageincreases because capacitance decreases, the thickness of the sheath 404decreases, because the V_(p)−V_(DC) value decreases. Thus, moving theadjustable tuning ring 150 affects the shape of the sheath 404, which inturn controls the direction of plasma ions.

Referring back to FIG. 1, control of the adjustable tuning ring may becontrolled by a controller 191. The controller 191 includes programmablecentral processing unit (CPU) 192 that is operable with a memory 194 anda mass storage device, an input control unit, and a display unit (notshown), such as power supplies, clocks, cache, input/output (I/O)circuits, and the liner, coupled to the various components of theprocessing system to facilitate control of the substrate processing.

To facilitate control of the chamber 100 described above, the CPU 192may be one of any form of general purpose computer processor that can beused in an industrial setting, such as a programmable logic controller(PLC), for controlling various chambers and sub-processors. The memory194 is coupled to the CPU 192 and the memory 194 is non-transitory andmay be one or more of readily available memory such as random accessmemory (RAM), read only memory (ROM), floppy disk drive, hard disk, orany other form of digital storage, local or remote. Support circuits 196are coupled to the CPU 192 for supporting the processor in aconventional manner. Charged species generation, heating, and otherprocesses are generally stored in the memory 194, typically as softwareroutine. The software routine may also be stored and/or executed by asecond CPU (not shown) that is remotely located from the processingchamber 100 being controlled by the CPU 192.

The memory 194 is in the form of computer-readable storage media thatcontains instructions, that when executed by the CPU 192, facilitatesthe operation of the chamber 100. The instructions in the memory 194 arein the form of a program product such as a program that implements themethod of the present disclosure. The program code may conform to anyone of a number of different programming languages. In one example, thedisclosure may be implemented as a program product stored on acomputer-readable storage media for use with a computer system. Theprogram(s) of the program product define functions of the embodiments(including the methods described herein). Illustrative computer-readablestorage media include, but are not limited to: (i) non-writable storagemedia (e.g., read-only memory devices within a computer such as CD-ROMdisks readable by a CD-ROM drive, flash memory, ROM chips, or any typeof solid-state non-volatile semiconductor memory) on which informationis permanently stored; and (ii) writable storage media (e.g., floppydisks within a diskette drive or hard-disk drive or any type ofsolid-state random-access semiconductor memory) on which alterableinformation is stored. Such computer-readable storage media, whencarrying computer-readable instructions that direct the functions of themethods described herein, are embodiments of the present disclosure.

While the foregoing is directed to specific embodiments, other andfurther embodiments may be devised without departing from the basicscope thereof, and the scope thereof is determined by the claims thatfollow.

What is claimed is:
 1. A process kit for a substrate processing chamber, the process kit comprising: a first ring having a top surface and a bottom surface, the bottom surface supported by a substrate support member, the bottom surface at least partially extending beneath a substrate supported by the substrate support member; an adjustable tuning ring positioned beneath the first ring, the adjustable tuning ring having a top surface and a bottom surface, the top surface of the adjustable tuning ring and the first ring defining an adjustable gap; and an actuating mechanism interfaced with the bottom surface of the adjustable tuning ring, the actuating mechanism configured to alter the adjustable gap defined between the bottom surface of the first ring and the top surface of the adjustable tuning ring.
 2. The process kit of claim 1, wherein the adjustable tuning ring is formed from a conductive material.
 3. The process kit of claim 1, wherein the adjustable gap is adjustable between 0 and 4 mm.
 4. The process kit of claim 1, wherein the actuating mechanism comprises: a lift pin having a first end and a second end, the first end of the lift pin contacting the bottom surface of the adjustable tuning ring, the second end of the lift pin in communication with a lift mechanism.
 5. The process kit of claim 1, wherein the adjustable tuning ring comprises: an annular body; a cavity formed in the annular body, the cavity formed in the bottom surface of the annular body; and an access orifice formed in the annular body, the access orifice extending from the top surface of the adjustable tuning ring into the cavity.
 6. The process kit of claim 5, wherein the actuating mechanism is a screw disposed at least partially in the cavity, the screw configured to be rotated through the access orifice to actuate the adjustable tuning ring.
 7. The process kit of claim 5, wherein the cavity has a first diameter and the access orifice has a second diameter, the first diameter being larger than the second diameter.
 8. The process kit of claim 1, wherein the actuating mechanism is configured to control a thickness of a plasma sheath formed between the plasma and the edge ring.
 9. A processing chamber, comprising: a substrate support member configured to support a substrate; and a process kit supported by the substrate support member, the process kit comprising: a first ring having a top surface and a bottom surface, the bottom surface supported by the substrate support member, the bottom surface at least partially extending beneath the substrate supported by the substrate support member; an adjustable tuning ring positioned beneath the first ring, the adjustable tuning ring having a top surface and a bottom surface, the top surface of the adjustable tuning ring and the first ring defining an adjustable gap; and an actuating mechanism interfaced with the bottom surface of the adjustable tuning ring, the actuating mechanism configured to alter the adjustable gap defined between the bottom surface of the first ring and the top surface of the adjustable tuning ring.
 10. The processing chamber of claim 9, wherein the adjustable tuning ring is formed from a conductive material.
 11. The processing chamber of claim 9, wherein the adjustable gap is adjustable between 0 and 4 mm.
 12. The processing chamber of claim 9, wherein the actuating mechanism comprises: a lift pin having a first end and a second end, the first end of the lift pin contacting the bottom surface of the adjustable tuning ring, the second end of the lift pin in communication with a lift mechanism.
 13. The processing chamber of claim 9, wherein the adjustable tuning ring comprises: an annular body; a cavity formed in the annular body, the cavity formed in the bottom surface of the annular body; and an access orifice formed in the annular body, the access orifice extending from the top surface of the adjustable tuning ring into the cavity.
 14. The processing chamber of claim 13, wherein the actuating mechanism is a screw disposed at least partially in the cavity, the screw configured to be rotated through the access orifice to actuate the adjustable tuning ring.
 15. The processing chamber of claim 13, wherein the cavity has a first diameter and the access orifice has a second diameter, the first diameter being larger than the second diameter.
 16. The processing chamber of claim 9, wherein the actuating mechanism is configured to control a thickness of a plasma sheath formed between as plasma and the edge ring.
 17. The processing chamber of claim 9, wherein the substrate support member comprises: a base; a cooling plate supported by the base; and an electrostatic chuck positioned on a top surface of the cooling plate.
 18. The processing chamber of claim 17, wherein the adjustable tuning ring is spaced from the cooling plate between about 0-2 mm.
 19. A method of processing a substrate, comprising: positioning the substrate on a substrate support member disposed in a substrate processing chamber; forming a plasma above the substrate; and adjusting a spacing between an adjustable tuning ring and an edge ring by actuating the adjustable tuning ring to change a direction of ions at an edge of the substrate.
 20. The method of claim 19, wherein actuating the adjustable tuning ring comprises: altering a thickness of a plasma sheath formed between the plasma and the edge ring. 